I'm just not sure that such a costume - the style and 'fit' of it, especially - would be something worn in a Japanese play.

I prefer my own idea of it being something especially devised for a ritual in an attempt to help Wolverine is helped to embrace the animal (while wearing it) and suppress the animal (when not wearing it). A way of trying to separate his animal and human aspects so that he can switch between them and not be dominated by either one.

Thing is, there's no need to separate the man from the animal but rather train the man to control the animal.

Spoiler!!! Click to Read!:

In the script, Wolverine is the animal throughout the first act, killing dozens of people brutally. In the second act, through training, he learns to control the animal and kill like a warrior.

The scene with the costume is brilliant because at first Mariko's not sure its him. When she locks eyes with him through the mask she realizes it is him and is immediately mortified to see the man she loves slaughter all those people.